1. Field of the Invention
The present invention relates to a dual accelerometer which comprises a mounting base and two electro-mechanical transducers arranged one upon the other in between the mounting base and a common seismic mass and an additional seismic mass between the two transducers.
2. Background and Prior Art
Accelerometers are known in which the axis of sensitivity of dual transducers are mutually perpendicular, whereby the transducers measure components of acceleration in mutually perpendicular directions. The adjustment of both transducers to the same sensitivity is achieved by forming each transducer from a relatively high number of individual peizoelectric elements. The number and the individual sensitivity of the elements being so matched and selected that both transducers have the same sensitivity. The precision of the matching of the sensitivities of such transducers is very limited since the sensitivity of each individual transducer may vary during the manufacturing process. This sensitivity matching procedure not only makes transducer manufacture difficult, it also requires the utilization of a relatively high number of piezoelectric elements in each transducer so that the production of an accelerometer based on this method becomes expensive.
U.S. Pat. No. 4,213,114 discloses the use of two identical accelerometers, each with the same axis of sensitivity, that is monoaxial accelerometers, for controlling vibrations of rotating machines, such as aircraft engines. Each transducer of such accelerometers is connected to an independent measuring circuit in order to improve the redundancy of the measuring device. Unfortunately, this construction results in a relatively expensive, voluminous and heavy device. In order to be mounted in aircraft engines, accelerometers should preferably have small dimensions and be of light weight.
U.S. Pat. No. 3,744,322 discloses the use of an angular velocity sensor utilizing the Coriolis force. The sensor comprises two proof masses arranged between piezoelectric transducers. These transducers are excited by an a.c. signal having a frequency of 5 kHz which functions to set the masses into vibration along the axis of rotation of the sensor. The movements of the masses along the axis of rotation are 180.degree. out of phase with one another. The device further comprises pairs of sensors sensitive to shear forces in two directions perpendicular to one another and to the axis of rotation of the sensor. However, such an angular velocity sensor does not include an additional seismic mass between the transducers so that the sensitivity of the transducers may be easily matched to deliver a signal of desired value when both transducers are submitted to a common acceleration.